This invention relates to a process of steam reforming hydrocarbons to produce a gas containing carbon oxides and hydrogen and to a reactor assembly for carrying out the process.
In the majority of steam reforming processes proposed or in industrial use, the endothermic steam hydrocarbon reaction typified by EQU CH.sub.4 +H.sub.2 O.fwdarw.CO+3H.sub.2 .DELTA.H=49.3 kcal/gmol
is carried out over a catalyst disposed as a bed in tubes externally heated in a combustion furnace and heat is recovered by producing steam. However, in a long known and occasionally industrially used process, the hot reformed gas leaving the catalyst bed is withhdrawn through an inner tube within the catalyst bed, so that heat is exchanged between that hot gas and reactants reacting over the catalyst. Examples of this process are described in GB-A-330872, U.S. Pat. No. 4,271,086 and our EP-A-124226. This arrangement of the reaction zone, referred to commonly as "bayonet-tube" or "field tube" or "double-pass" primary reformer is evidently advantageous in providing a useful heat recovery and in avoiding construction problems due to differential thermal expansion.
We have now realized that the heat transfer properties of the double pass type of reformer can be improved in a way that is especially advantageous when the source of heat is not independent of the reforming stage.